One aspect of this invention relates to stabilization agents which, through attraction to solid surfaces of mineral particles, such as clay for example, of a size less than about 7 microns, cause normally hydratable clay to become permanently stable. Another aspect of this invention relates to treating solutions for well bores passing through natural geological formations which comprise clay or other fine particulate matter, the treating solutions comprising an oxygenated polyamine composition in a diluent. A still further aspect of this invention relates to a method for treating clay formations adjacent boreholes in a manner which stabilizes clay materials present in the formations and subsurface layers penetrated thereby.
Clays, and claylike materials which are subject to swelling and/or dispersion with subsequent loss of permeability and reduction in mechanical strength sometimes present major problems in recovering minerals from geological formations. Clay containing bodies are often substantially impermeable or at least have a low permeability to fluids or lose some or all of the permeability that they may possess when they are subjected to the actions of liquids such as water, and water containing emulsions. Thus, clay contained in formations present in or adjacent to boreholes can be subject to swelling, disruption and/or migration when producing fluids such as hydrocarbons, or when water, gels and other types of stimulation fluids are injected into the geological formation. Furthermore, clay in the form of a clay containing mud is sometimes introduced into a formation where it is not naturally present.
Clays which are present in the geological formation can reduce the permeability of that formation by swelling and/or migrating to form bridges or blockages in the pores of the formation or in perforations in casing screens and similar articles used in well completions. Such swelling and migration results when aqueous liquids used (or produced) during oil production operations come into contact with the clay materials. Furthermore, clay which is used as a component of drilling muds can invade the formation during the drilling of the borehole. For example, high swelling montmorillonite is often used in drilling muds because of its ability to create a low permeability filter cake on the formation face, among other reasons. However, such a low permeability zone may be created, undesirably, within the formation in the vicinity of the borehole because of invasion therein by the drilling mud.
Among the clays which may be present originally in natural geological formations, or may have been introduced therein, and which can be effectively treated in accordance with the present invention are clay materials of the smectite (montmorillonite) group such as montmorillonite, saponite, nontronite, hectorite, beidellite, and sauconite; the kaolin group such as kaolinite, nacrite, dickite, endellite and halloysite; the illite (hydrous-mica) group such as hydrobiotite, glauconite, and illite; the chlorite group (both 7 and 14 angstrom basal spacings) such as chlorite, greenalite and chamosite; clay minerals not belonging to the above groups such as vermiculite, palygorskite (attapulgite) and sepiolite; and mixed-layer (both regular and irregular) varieties of the above minerals. The clay content of the formations can be comprised substantially of a single species of a clay mineral or several species, including the mixed-layer types of clay. Of the clay minerals commonly encountered in the drilling of wells in natural geological formations which can be productive of the difficulties herein noted and which can be treated effectively in accordance with the present invention are clay minerals selected from the class consisting of montmorillonite group, illite (hydrous-mica group), chlorite group and kaolin group. It will be understood that the clay-containing formations treated in accordance with the invention need not be composed entirely of clay but may contain other mineral components associated therewith. Formations which consist largely of clay can, upon contact with water, or water containing fluids, swell and these swelled clays can develop pressures in the order of several thousand pounds per square inch.
The clay materials defined above occur as minute, platelike, tubelike and/or fiberlike particles having an extremely large surface area compared to that of an equivalent quantity of a granular material such as sand. This combination of small size and great surface area results in a high surface energy with attendant unusual surface properties and extreme affinity for surface active agents. The structure of some of these clays, as for instance montmorillonite, can be pictured as a stack of sheetlike three layer lattices which are weakly bonded to each other and which are expanded in the "C" crystallographic direction by water or other substances which can penetrate between the sheets and separate them.
All clay materials have ion exchange properties. Thus for example montmorillonite has a cation exchange capacity of from about 90 to 130 milliequivalents per 100 grams of pure clay, illite from about 20 to about 40 milliequivalents, and kaolinite from about 5 to about 15 milliequivalents. Under ordinary oil well conditions the ion exchange reactions between the clays and substances associated with the clays and capable of reacting therewith are essentially reversible in nature.
The properties of clays vary widely with the cations occupying the base exchange positions or sites. A "base exchange position or site" can be defined as an area, in this instance on the surface of a clay crystal, which has associated with it an exchangeable cation. Among the cations which are generally found on the base-exchange position or site can be mentioned sodium, potassium, calcium, magnesium, iron, hydrogen and the like. These cations are believed to be held on the clay surface by ionic forces.
In addition to clay materials, other fine mineral particles of a size less than about 7 microns can cause blockage problems during production operations. It is therefore desirable to stabilize these "fines" as well as any clay particles which may be present in a given formation.
In the past, well bore holes have been treated with clay stabilization agents in an effort to overcome the above described types of problems. For example, U.S. Pat. No. 2,761,835 discloses a method of stabilizing a clay containing body which includes contacting the clay with substituted ammonium ions derived from aliphatic nitrogen compounds of a specific nature. However, these types of clay stabilization agents tend to alter the wettability of the formation which can cause problems during completion and production. Specifically these, and other types of stabilizing agents employed in the past, can cause the formation to become "oil wet" as opposed to "water wet". Those skilled in the art believe it to be advantageous to production if the producing formation remains "water wet". Finally, many of the clay stabilization agents which have been available heretofore (such as alum based compositions, for example) have not been permanent in nature since the beneficial effects thereof are lost upon subsequent treatments of the formation with acid and/or fracturing fluids.
Further, epichlorohydrin-dimethylamine copolymers have been used in the past in relatively unrelated applications. For example, U.S. Pat. No. 4,001,486 discloses epichlorohydrin-dimethylamine copolymers which are useful in a method for coagulating synthetic rubber particles. The disclosures of that patent pertaining to the copolymers disclosed to be useful in the present invention are hereby incorporated by reference.
Thus, a clay stabilization additive which would have the desired effect of shrinking hydrated clay and preventing swelling and hydration of nonhydrated clay upon contact with water contained in well treatment solutions would be greatly advantageous in the oil well industry. Further, a clay stabilization agent which is relatively easy to handle and use, is miscible with water and readily soluble in brines and acids, does not alter the wettability of formation surfaces, which provides substantially permanent clay stabilization effects, and which is effective over a wide pH range, would be desirable.